SQL Select - 检查值是否在逗号分隔列表中 - PHP [duplicate]

I'm wanting to create a sql select statement that will grab rows if a given value is in a comma separated list in one of the columns of the database table.

Example Table...

id | courses
1   | 5, 8, 15, 19

I want to do something like this
$course_num = 5;
$sql = "SELECT * FROM courses WHERE $course_num IS IN courses";

1.) I don't think the "IS IN courses" part is legit. How can I do this?
2.) For my code above, I would want to return the row because of the "5" in courses, not because of the "15". So, if $course_num = 9 no rows should be returned.

Thanks for your help.

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By adding comma in searched occurrence

SELECT * 
FROM courses 
WHERE concat(', ',course,',') like '%, 5,%'